I. Field
The following description relates generally to communication systems, and more particularly to a method and apparatus for establishing communications in low signal to noise ratio environments.
II. Background
In certain wireless systems, before two devices can communicate, they must be paired. The pairing process typically includes an acquisition process. In most cases, the acquisition process for wireless communications under low signal-to-noise ratio (SNR) environments is a difficult problem as there are several hurdles. Two issues to consider include the presence of clock drift and the possible existence of interference.
During the communication process between two devices, there may exist clock drift from the difference between the two clocks of two different devices. The presence of clock drift reduces the effectiveness of the transmissions between devices as the timing for signals often need to be managed within a small tolerance, especially in high speed communications. Clock drift exists because of hardware manufacturing tolerances and, to some extent, environmental factors. However, compensation for clock drift by another device may be achieved more efficiently if the other device is able to have an estimate of the clock drift before the compensation process.
Preamble sequences for wireless communications are used as part of the acquisition process. One purpose for the use of the preamble is to allow time for the receiver in each node to achieve lock of the receiver's Digital Phase Lock Loop, which is used to synchronize the receive data clock to the transmit data clock. At the point when the first bit of the preamble is received, each receiver may be in an arbitrary state. During the course of detecting the preamble, it learns the correct phase, but in doing so it may need to acquire a number of samples. The number of samples that need to be captured and analyzed for proper acquisition is dependent on the received signal quality, which is affected, among others, by the amount of clock drift.
Consequently, it would be desirable to address one or more of the deficiencies described above.